There are two crucial items to have in AD RMS. One is a good back up of the AD RMS databases. The other is the cluster key password. With these two things one can recover from most disasters.

Disaster recovery scenarios aside the most common need for the cluster key password is installation events. When upgrading from RMS v1 to AD RMS or adding a new server to the existing RMS/AD RMS cluster the cluster key password is needed.

If the password is unknown/forgotten, or needs to be changed, it is an easy undertaking. The task is accomplished via the AD RMS console. The main caveat of changing the cluster key password is that it must be done on each member of the AD RMS cluster. 

Below are the screenshots of going into the AD RMS cluster and changing the cluster key password.